This invention relates to a new process for separating pure 4,4'-dichlorodiphenylsulfone from the reaction mixture containing 4,4'-dichlorodiphenylsulfone and the isomers thereof, namely 2,4'-isomer and 3,4'-isomer.
The 4,4'-dichlorodiphenylsulfone is useful as intermediates for medicines and synthetic resines.
Some processes for the production of 4,4'-dichlorodiphenylsulfone are known, for example, by the reaction of monochlorobenzene with dimethyl pyrosulfate and sulfuric anhydride, by the reaction of p-chlorobenzenesulfonic acid and monochlorobenzene in sulfuric acid, and by the reaction of p-chlorobenzenesulfonyl chloride and monochlorobenzene in the presence of ferric chloride as a catalyst.
Japanese Patent Publication No. 11,817/1962 and U.S. Pat. No. 3,309,409 disclose the process for the separation of the product by adding a reaction mixture to water or aqueous alkali to precipitate the product. In this method, when adding the reaction mixture containing a large amount of acidic materials to water, the precipitate of the product is contaminated by the acidic materials, the isomers (2,4'-, 3,4'-) and other impurities.
U.S. Pat. No. 3,415,887 discloses the process for the separation of the product by dissolving a reaction mixture in methylene chloride, neutralizing acidic materials by aqueous alkali, and then evaporating the separated methylene chloride solution to dryness. Also in this method, the contamination of the product by the isomers is not avoidable because the solubility of the product to methylene chloride is extremely high and the product is necessarily obtained as evaporation residue.
In the process of U.S. Pat. No. 3,334,146, the reaction mixture is dissolved in monochlorobenzene and the solution is washed with water. The solution is cooled to precipitate the product. In this method, considerably pure product is obtained, however the precipitation yield is low and the recovery of the product from the mother liquor is complicated.
The inventors have found that trichloroethylene and tetrachloroethylene are the most advantageous solvents for extraction and recrystallization of 4,4'-dichlorodiphenylsulfone, and have accomplished an industrially advantageous process for the separation of 4,4'-dichlorodiphenylsulfone.
It is the object of this invention to provide an industrially advantageous process for separating highly pure 4,4'-dichlorodiphenylsulfone from the reaction mixture which contains 2,4'-isomer and/or 3,4'-isomer as by-products.
Other and further objects, features and advantages will appear more fully from the following discription.